Optical touch panel systems have been developed for use as input mechanisms for display devices. Generally, arrays of light emitters and detectors are mounted around the display screen of the display device to establish a plane of light beams passing across and near the display screen. One array of emitters is positioned across the bottom of the screen to extend in an "X" direction. These emitters may be referred to as X emitters. An array of light detectors, referred to as X detectors, is positioned across the top of the screen. Each X emitter is aligned with an X detector.
Another array of light emitters is positioned across one side of the screen to extend in a "Y" direction. These emitters may be referred to as Y emitters. An array of light detectors, referred to as Y detectors, is positioned across the other side of the screen. Each Y emitter is aligned with a Y detector.
Typically, the X emitters and X detectors are sequentially scanned from one side of the display screen to the other. The output signals of the scanned X detectors are monitored to detect an interruption of any X emitter light beam, the interruption indicating the presence of a finger or stylus near the display screen. The Y emitters and Y detectors are also sequentially scanned from the top to the bottom of the display screen. The output signals of the Y detectors are monitored to detect an interruption of any Y emitter beam.
Whenever a stylus is placed near the display screen, data representing the location of the interrupted X emitter beam and of the interrupted Y emitter beam are transmitted to the display device controller. The data represent the X and Y position coordinates of the stylus. The display is changed in a predetermined manner in response to the stylus position data.
To locate a stylus, the sequential scanning technique employed with conventional optical touch panel systems requires an amount of time of the order N, wherein N is the number of light detectors in the detector array having the largest number of detectors. For most applications, it is desirable to minimize the time required to locate the stylus.